Not being able to see another MORE THAN two f/stops' worth of dynamic range?
Erm...
Not disagreeing with your overall conclusion, Derrel, but this part stands out as a bit silly.
1) It's only 2 stops higher at ISO 100. Even at ISO 200, it's already down to only about 1.3 stop better and by 400, more like 1/2 a stop. Suggesting that the D610 is just in general 2 stops better is very misleading.
2) The difference is between 12 and 14 stops, and the great majority of scenes we shoot have less than 13 stops of dynamic range, so in
most cases, no you in fact
cannot see the difference, because both capture all that is needed! An overcast day is usually like 3-5 stops of range. A sunny day with cast shadows (say, 3PM) is about 7 stops of range usually. Even snow and sand contrasted with dark water or rocks on a sunny day is unlikely to get above 12.
14 stops of dynamic range is only relevant in extreme circumstances like fully backlit sunsets or like a dark room with only a single window that you want to see details through, etc.
And when you combine #1 and #2 it's even more narrowly relevant. For example, it's pretty unlikely that you would be shooting at ISO 100 in that dark single window room. So if you're at 400 or something to get the dark details without blur,
you wouldn't even HAVE the 2 stop advantage then when you needed it anyway... In the sunset example you may or may not have the advantage when you need it either, depending on your desired artistic aperture.
After a certain point, more dynamic range gets pretty useless. We could definitely still use improvements at the high ISO end, and at low, 14 is sometimes handy. But in the future, if/when we are looking at differences like 16 vs 18, it's going to become more and more irrelevant, and it's already getting there.